Abstract : The quadrature-sampling technique, which obtains samples of the quadrature components of a high-frequency band-limited waveform by direct sampling of the waveform, is shown to lead to an exact interpolation formula. In this formula, the quadrature components of the signal are represented explicitly by low-pass interpolation formulas that greatly facilitate digital processing of the signal when compared to commonly used sampling formulas. For example, the amplitude modulation (envelope) and phase modulation of a signal can be computed directly from these quadrature components. (Author)